Prions are highly infectious proteinaceous agents responsible for several devastating and invariably fatal neurodegenerative diseases. Examples include Creutzfeldt-Jacob disease and kuru in humans, bovine spongiform encephalopathy in cattle, and chronic wasting diseases in elk and deer. The broad and long-term objective of our research is to further our molecular understanding of prions and prion diseases. [unreadable] [unreadable] [PSI+] is a yeast prion that increases translational read-through of nonsense codons. Like mammalian prions, yeast prions consist entirely of protein. [PSI+] is formed by self-replicating amyloid conformers of Sup35, which ultimately result in the formation of amyloid fibrils, a hallmark of prion diseases. Most interestingly, the inheritance, propagation, and elimination of [PSI+] are governed by the Hsp104 molecular chaperone. First discovered as an essential component in the yeast stress response, Hsp104 is an ATP-dependent protein- remodeling factor, which can rescue stress-damaged proteins from a previously aggregated state. While the ability to disaggregate proteins is shared with bacterial ClpB, ClpB neither promotes propagation nor facilitates elimination of [PSI+], suggesting that prion-remodeling and protein-disaggregating activities are mechanistically distinct. [unreadable] [unreadable] The goal of this proposal is to provide a detailed mechanistic understanding of the role of Hsp104 in prionogenesis. The following specific aims are proposed: (1) to determine the high-resolution crystal structure of Hsp104, (2) to dissect the biochemical mechanism of Hsp104 prion-remodeling activity, and (3) to determine the 3D structure of an Hsp104/Sup35 complex. To achieve our goals, we will combine three-dimensional structural studies with biochemical and high-throughput proteomic approaches. The combination of these techniques will provide substantial new insight into the mechanism of prion remodeling, an activity unique to Hsp104. Moreover, our proposed studies may also provide answers to why molecular chaperones cannot prevent prion infections, and may open new avenues in the search for a potential treatment of prion infections and other protein misfolding diseases. [unreadable] [unreadable] Prions are unconventional, highly infectious agents, responsible for several devastating and invariably fatal neurodegenerative diseases collectively known as transmissible spongiform encephalopathies. Molecular chaperones provide the first line of defense against prion infections and other protein misfolding diseases. Here we will investigate the structure and mechanism of Hsp104, a prion-remodeling factor and essential molecular chaperone of the stress response. [unreadable] [unreadable] [unreadable]